A House of Commons Standard Note (SN/PC/05085) says " the Government will decide what its priorities are and seek the co-operation the Opposition in getting legislation through. In doing so there will invariably be sacrifices to be made. Some Bills might be lost completely, others might be progressed quickly but in a much-shortened form. A lot will depend on where the Bills are in the legislative process and whether or not they are controversial."
Once business is completed (perhaps on Thursday 8th April) Parliament would be prorogued. It would then be dissolved (probably on Monday 12th, the last date for this in the election timetable - see House of Commons Research Paper 09/44)
One circumstance (other than Gordon Brown deciding not to call a May 6th election) would lead to a different date. The death of the Queen during the election period. s20 Representation of the People Act 1985 would postpone the election day by two weeks (20th May).